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In the Name of God بسم الله

29 or 30 days

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Posted (edited)

:salam:

I would like to understand what determines a month being 29 or 30 days.

Is there a logic behind it ? 

Being a complete ignorant, I would think it is all about a sighting issue : two countries beginning a month on a same day, if one sees the moon at the end of the month then it may be 29, whereas the second country will wait, making it 30. So some kind of 'tolerance' given by the Prophet (sawas). 

All that so 12 months can fit in a 354/355-day year. 

Am I correct ? 

 

Edited by realizm
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8 minutes ago, realizm said:

:salam:

I would like to understand what determines a month being 29 or 30 days.

Is there a logic behind it ? 

Being a complete ignorant, I would think it is all about a sighting issue : two countries beginning a month on a same day, if one sees the moon at the end of the month then it may be 29, whereas the second country will wait, making it 30. So some kind of 'tolerance' given by the Prophet (sawas). 

All that so 12 months can fit in a 354/355-day year. 

Am I correct ? 

 

Salaam,

This might relate to your topic:

https://www.iqraonline.net/four-methodologies-for-sighting-the-new-moon/

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Wa alaikum as salam

If you are asking why the visibility of the crescent sometimes appears after 29 days and sometimes after 30, it is simply a question of timing. 

Just as you have a sun rise and a sun set time, there are also moon rise and moon set times. 

To sight the moon, it should be at a certain angle within a certain time frame (after sunset so that it is visible). If these criteria are fulfilled on the 29th day then the crescent is sighted and the month ends.

If not (angle is still too small, or moon has already set before the sun etc) then it won't be visible until the next day (by which time the angle has become more favorable for visibility and the rising and setting times have spread further apart).

The moon itself obviously doesn't change shape, it is simply the visibility that evolves in a cyclical manner throughout the month. 

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2 hours ago, Mahdavist said:

Wa alaikum as salam

If you are asking why the visibility of the crescent sometimes appears after 29 days and sometimes after 30, it is simply a question of timing. 

Just as you have a sun rise and a sun set time, there are also moon rise and moon set times. 

To sight the moon, it should be at a certain angle within a certain time frame (after sunset so that it is visible). If these criteria are fulfilled on the 29th day then the crescent is sighted and the month ends.

If not (angle is still too small, or moon has already set before the sun etc) then it won't be visible until the next day (by which time the angle has become more favorable for visibility and the rising and setting times have spread further apart).

The moon itself obviously doesn't change shape, it is simply the visibility that evolves in a cyclical manner throughout the month. 

True, that was my understanding.

Yet there is an issue with 354 or 355 days of the year. Since shape and rotation are, as you said, unchangeable, then how come we come to only one day of discrepancy from year to year ?

It's like admitting 6 months of 29 day and 6 months of 30 days (174+180=354). 

If all moons are visible at 30 days then that would make a 360-day-year right? 

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4 hours ago, realizm said:

Yet there is an issue with 354 or 355 days of the year. Since shape and rotation are, as you said, unchangeable, then how come we come to only one day of discrepancy from year to year ?

It's like admitting 6 months of 29 day and 6 months of 30 days (174+180=354). 

If all moons are visible at 30 days then that would make a 360-day-year right? 

Ok I understand what you mean. I am assuming (to be checked if this is accurate) that in reality the cycle is not 29 or 30 days, rather something in the middle 29.x , and so if in month A you 'just missed' the crescent by a few minutes/hours on day 29 (therefore 30-day month) then most likely (but not necessarily) on day 29 of the next month it's visibility will be better since it is an 'older' moon (in this case the month is 29 days).

Or in other terms, 12 rotations of the moon will always fall between 354 and 355 days in duration. This means that the 12 months cannot all be only 29 days nor only 30 days, rather they will be split into 29 and 30-day months. 

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